Cheesy Harvest Casserole

Name: Cheesy Harvest Casserole
Ingredients: 10 ounces butternut squash, peeled and in ½” cubes; 1/2 medium onion, diced; 1 tablespoon water; 6 ounces evaporated milk; 1/2 teaspoon mustard powder; 1 cup Gruyere cheese, shredded and divided into 2 half cups; 1 cup Monterey Jack cheese, shredded and divided into 2 half cups; 1 cup sharp cheddar cheese, shredded and divided into 2 half cups; 1/4 teaspoon kosher salt; 1 box brown rice pasta (I like the one from Trader Joe's; 1 tablespoon canola oil; 1 pound ground chicken or turkey (you can omit this to make it vegetarian); kosher salt; pepper; 1 1/2 cups chopped tomatoes (I use Pomi chopped tomatoes)